1. Field of the Invention
The present invention relates to a solid-state image pickup apparatus including a solid-state image sensor in which photosensitive cells for photoelectric transduction are arrayed in a so-called honeycomb arrangement, and a method of adjusting the outputs of, e.g. an array of photosensitive cells, each of which includes a set of photosensitive regions different insensitivity from each other, for compensating for sensitivity errors.
2. Description of the Background Art
Generally, a solid-state image pickup apparatus is apt to generate moiré and other false signals. Japanese Patent Laid-Open Publication No. 136391/1998, for example, discloses a solid-state image pickup apparatus configured to receive the increased quantity of incident light with pixels densely arranged, thereby promoting efficient receipt of light. The apparatus taught in this document provides a new structure that optimizes spatial sampling of an image and is referred to as a honeycomb pixel arrangement.
In the honeycomb pixel arrangement, assuming that the distance between nearby pixels on the same row or the same column is defined as a pitch, then pixels around a given pixel each are shifted from the given pixel by half the pitch in the direction of row and/or the direction of column. In a CCD (Charge-Coupled Device) type of solid-state image sensor having the honeycomb pixel arrangement, vertical transfer registers constitute vertical transfer paths extending zigzag in such a manner as to skirt round the pixels. Color filter segments are assigned to, among the pixels, actual pixels that actually exist. The pixels, or photosensitive cells, photoelectrically transduce light incident thereto through the color filter segments to generate signal charges having color attributes. The signal charges are then sequentially routed through the vertical transfer registers and horizontal transfer register, which constitutes a horizontal transfer path disposed perpendicularly to the vertical transfer paths, to an output amplifier. The output amplifier performs Q/V conversion for outputting voltage signals in the form of analog signals.
Subsequently, the analog signals are subjected to signal processing. First, a correlation between pixel data is determined with consideration given to the colors of actual pixels. More specifically, pixel data of a color in question closely correlated to each other are used to estimate pixel data at a virtual pixel, defined as a pixel at which the actual pixels are not positioned, and pixel data at actual pixels of a color different from the color in question. Subsequently, one of such pixel data appearing in a direction closer in correlation than the remaining pixel data is used for interpolating virtual pixels. Such interpolation successfully reduces false signals. Further, the pixel data are successfully broadened in frequency band, enhancing resolution.
It has also been proposed to use the honeycomb pixel arrangement for further enhancing the resolution of an image and broadening the dynamic range of image signals generated. In accordance with a specific conventional scheme directed toward this object, the photosensitive area of the individual photosensitive cell is divided into a major region and a subregion different in size from each other, so that signal charges are read out from the two regions independently of each other. This scheme broadens the dynamic range utilizing the difference in sensitivity between the main and subregions. In a usual reading mode, the signal charges of the main and subregions are mixed together and read out in the conventional manner.
Processing for broadening the dynamic range utilizes the sensitivity difference and the saturation in a pair of photosensitive regions.
The sensitivity difference between a pair of photosensitive regions of a photosensitive cell depends upon, for example, the difference in area between optical openings or apertures formed over the regions. More specifically, paying attention to a single photosensitive cell, an optical opening for passing incident light is formed smaller in area than the entire photosensitive region of the cell. Therefore, so long as the photosensitive region is relatively large in area, as with the main region, even if a mask for fabricating the opening is slightly set off during manufacturing in a planar direction of the region, the photosensitive region having the opening finished will be able to successfully absorb the affect by the off-set mask due to the relatively large area thereof.
However, an opening area formed in the subregion of a photosensitive cell, which is smaller in area than in the main region, is relatively small and therefore susceptive to the offset of the mask for fabrication the opening. As a result, an error may often be introduced in the optical sensitivity of the subregion in dependence upon the degree of accuracy in aligning the mask. If such a sensitivity error is remarkable, then it is likely that the signal processing for broadening the dynamic range is not practicable at all.